Fix sheet number access

getPageNumber is actually asking for the parent path rather than the
sheet path itself.  Without this, we don't match the cached page number
and instead match against the virtual page number that is position
dependent

Fixes https://gitlab.com/kicad/code/kicad/-/issues/21296

(cherry picked from commit 8edc7b8b40)

eeschema/sch_sheet_path.cpp

@@ -847,16 +847,13 @@ void SCH_SHEET_LIST::SortByHierarchicalPageNumbers( bool aUpdateVirtualPageNums
             SCH_SHEET* sheet_b = b.at( common_len );
 
             // Create partial paths to get to these sheets for page number comparison
-            KIID_PATH path_a, path_b;
-            for( size_t i = 0; i <= common_len; i++ )
-            {
-                path_a.push_back( a.at( i )->m_Uuid );
-                path_b.push_back( b.at( i )->m_Uuid );
-            }
+            KIID_PATH ancestor;
+            for( size_t i = 0; i < common_len; i++ )
+                ancestor.push_back( a.at( i )->m_Uuid );
 
             // Compare page numbers - use the last sheet's page number
-            wxString page_a = sheet_a->getPageNumber( path_a );
-            wxString page_b = sheet_b->getPageNumber( path_b );
+            wxString page_a = sheet_a->getPageNumber( ancestor );
+            wxString page_b = sheet_b->getPageNumber( ancestor );
 
             int retval = SCH_SHEET::ComparePageNum( page_a, page_b );